A plain bearing, which is a representative sliding member, has a structure in which a bearing-alloy layer consisting of copper alloy or aluminum alloy and referred to as a lining and an overlay layer consisting of a soft metal are laminated on a backing steel sheet. The soft-metal overlay is utilized as a compatibility layer, and is deposited on the plain bearing-alloy layer usually by electroplating. As is shown in FIG. 1 of Patent Document 1 (Japanese Patent No. 3463809), the bearing parts as a whole are immersed in the plating liquor so as to electrolytically precipitate a Pb-based overlay on the plain bearing alloy.
Conventionally, a Pb-based alloy has been usually used for producing an overlay layer. However, since Pb is environment-polluting material, a Bi-based overlay has been proposed. That is, Pb is replaced with Bi.
For example, Patent Document 2 (Japanese Unexamined Patent Publication (kokai) No. 2004-308883) proposes a sliding member having the above-described laminated structure. That is, a plain bearing alloy used is Cu or Al-based alloy, and a Bi or Bi-alloy plated layer is used for an overlay layer. This Bi or Bi-alloy plated layer is texture controlled by the PR electrolytic method such that an orientation index of (202) plane amounts to 30% or more and amounts to the highest value as compared with the other planes.
According to Patent Document 3 (Japanese Patent No. 3693256), a plain-bearing Cu or Al alloy layer is formed on a backing metal of a steel sheet, and then a Bi—Cu based overlay layer is formed by PR electrolytic plating.